Nitrogen-containing compounds in petroleum fractions can adversely affect end products. For example, nitrogen compounds can adversely affect the storage stability and octane value of naphthas and may extent, since it lowers the potential for NO.sub.X formation during subsequent poison downstream catalysts. Nitrogen removal improves air quality to some fuel combustion. Crude and other heavy petroleum fractions are typically subjected to hydrodenitrification in a hydrotreater to significantly reduce nitrogen compounds prior to being subjected to further processing by first and second stage hydrocracking. The first stage hydrocracker can also be used to further reduce nitrogen compounds in a feedstock prior to passing it to a second stage hydrocracker. Second stage hydrocracking catalysts can be adversely affected by high levels of nitrogen compounds in their feedstock.
First stage hydrocrackers need both good hydrodenitrification activity and cracking activity. Hydrocracking catalysts frequently comprise metals supported on amorphous silica-alumina supports which provide an acid cracking function. These silica-alumina materials are seriously poisoned by organic nitrogen species. A catalyst with good hydrodenitrification activity and which was provided with an enhanced cracking function that was not poisoned by organo nitrogen compounds could be used not only in hydrotreaters, but also in first stage hydrocrackers.
Applicant has developed a method for improving the hydrodenitrification activity and cracking activity of a hydrotreating/first stage hydrocracking catalyst. A more active catalyst can be operated at a lower temperature to obtain the same degree of nitrogen conversion as a less active catalyst. A lower operating temperature will prolong catalyst life and decrease operating expenses.
The prior art discloses several examples of modifications to catalysts using silicon compounds as modifying agents. U.S. Pat. No. 4,038,337, issued Jul. 26, 1977, discloses the treatment of alumina with silicon compounds to provide a catalysts which are more active and selective for olefin isomerization. U.S. Pat. Nos. 4,013,589 and 4,013,590 and Reissue number 30,668 all disclose methods for improving the thermal and mechanical properties of alumina by treating it with silicon compounds. U.S. Pat. No. 3,089,845 discloses that the properties of naphtha catalysts are improved by treating with a silicon compound such as tetraethyl orthosilicate. U.K. patent number 2,121,430 discloses also the treatment of isomerization catalysts by the treatment with silicon compounds such as ethyl orthosilicate.